FWIW My gravel bike has a 4III single sided PM, road bike on trainer has a rotor single sided PM and the bike I actually ride on the road has a rotor 2inpower dual sided PM, I am usually 56/44 LR balance, so my numbers on the dual sided PM are always lower than my single sided PM’s.
I have a Quarq double sided PM on the gravel bike and Assiomas on the road bike. At endurance power, both report a 52-53/48-47 L/R power balance. That almost entirely disappears above 95% FTP, and at VO2 max power, I’m 51/52 right side dominant per the Assiomas, but the Quarq shows 50/50 dead on.
It used to bother me, but now I accept that a) these devices are not surgically accurate, b) I’m not perfectly symmetrical in shape and thus probably don’t function wholly symmetrically, and c) if I’m not in pain or discomfort, it doesn’t matter.
Just FYI, your Quarq isn’t really “double-sided”. Rather, it measures the total power (actually, torque) applied to the spider, then assumes that when, e.g., your left leg is descending, your right isn’t pulling up at all. This may be why it and your Assiomas disagree re. your L/R balance at higher power outputs.
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Three for me…
- SRAM Force (Quarq) spider on my road bike
- SRAM DUB left-sided on my gravel bike
- Wahoo Kickr
Only the first gives L/R balance, and it floats between 50/50 and 47/53 depending on fatigue level, effort, etc.
Yup, would be interesting especially since the landscape here is likely rather different than 5 years ago when I made that comment 
I hadn’t realised the comment was 5 years old😧
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Yeah, some people land on ancient topics from various paths and miss the date/age of the comments before replying. Everything old is new again. 